1. Field of the Invention
The present invention relates to a resilient leaning position-restoring device slidably disposed on the back support unit and characterized by resilient retraction. The resilient leaning position-restoring device comprises a resilient member coupled to the bottom of a chair back, such that resilient support given by the resilient member to the bottom of the chair back remains unaffected while the chair back is undergoing height adjustment thereof.
2. Description of the Prior Art
Office workers today stay at the office more often than at home, and thus, comfortable office chairs play an important role. However, a sitting posture that remains unchanged for a long period of time causes waist pain and back pain. The benefits of commercially available protective waistcoats designed for preventing waist pain and back pain are still unproven. Excessive customer loyalty to the protective waistcoats may not benefit the customers themselves. The sedentary life of computer users are susceptible to waist pain and back pain, and, thus, computer users need appropriate office chairs.
In general, the stress sustained by lumbar intervertebral discs is greater in a sitting posture with an upright trunk or with a trunk that inclines forward slightly (in a manner that the included angle between the trunk and the thighs is less than 90°) than it is in a standing posture. Hence, a sedentary posture (deficient in variation of posture) is likely to cause fatigue. As a result, after sitting for a long while, human beings move their bodies to relieve discomfort. In this regard, a chair back of a chair bears a portion of the body weight of a person sitting in the chair. Thus, the chair back reduces the person's lumbar stress, thereby allowing the person to relax his or her muscles. Hence, it is important for human beings to reduce waist pain, back pain, and fatigue when at work by enabling the waist to receive as much support from the chair back as possible. In case of a low seat of a chair, the lumbar vertebrae of a person sitting in the chair fail to come into contact with the chair back and thus fail to receive support therefrom. Likewise, if the chair back is too high or too low, the lumbar vertebrae of a person sitting in the chair cannot receive proper support from the chair back.
In view of this, a lumbar resilient leaning position-restoring device was developed for a height-adjustable chair back of an office chair of CN201641146. The resilient leaning position-restoring device essentially comprises a resilient support unit characterized by a resilient extension and retraction function and pivotally connected between the lower end of a height-adjustable chair back and the chair proper. The resilient support unit comprises a supporting inner rod and a supporting outer rod which are engaged with each other and can be resiliently retracted by a spring disposed therebetween. Springs are inserted and positioned at two pivotal ends of the resilient support unit for allowing the resilient support unit and the chair back to move in a predetermined direction. Hence, not only is the height of the chair back adjustable, but a person sitting in the chair can resiliently lean against the lower lumbar portion of the chair back. The resilient leaning position-restoring device not only allows sitters of different stature to lean against the chair back ergonomically, but also gives comfortable support to the sitters' waist and relieves the waist pain and back pain typical of a sedentary life.
However, to enable the chair back to descend and restore its position automatically, a spring is disposed between the support unit and the chair back for pulling the chair back downward and maintaining a force for pulling the chair back downward at any time. The above-mentioned has a drawback. That is, the bottom of the chair back retracts backward. Hence, it is necessary to provide another spring for not only offsetting the backward retraction of the chair back but also providing the resilient support for the sitters' waist. Hence, the structure in its entirety is not only intricate, but the two springs vary in resilience at the cost of the resilience of each other. Even if the chair back is ascending, the bottom of the chair back will retract slightly. Thus, there is inadequate resilient support for the sitters' waist, thereby greatly reducing the resilient support initially given to the sitters' waist and preventing better anticipated effect from being attained.